[BUG] caught IllegalArgumentException if batch size > 4096

[dockerzhang]

Describe the bug
caught IllegalArgumentException if batch size > 4096

To Reproduce
Steps to reproduce the behavior:

1. create a new topic --- t2
2. producer message with batch size 5000
./rdkafka_performance -P -t t2 -b 127.0.0.1:9092 -s 128 -a 1 -X batch.num.messages=5000 -c 1000000
3. consume
   ./rdkafka_performance -C -t t2 -b 127.0.0.1:9092 -G g2
4. See error

Expected behavior
consume correctly

Screenshots

[dockerzhang]

it may be caused by #175

[BewareMyPower]

Since continuous offset is already supported, this issue will no longer happen.